Quoting from the definition of VHOST_USER_SET_PROTOCOL_FEATURES in
vhost-user.rst:
> Only legal if feature bit ``VHOST_USER_F_PROTOCOL_FEATURES`` is present in
> ``VHOST_USER_GET_FEATURES``.
>
> .. Note::
> Slave that reported ``VHOST_USER_F_PROTOCOL_FEATURES`` must support
> this message even before ``VHOST_USER_SET_FEATURES`` was called.
To me, this could mean either of two things:
(1) If VHOST_USER_F_PROTOCOL_FEATURES hasn't been set, upon receiving
VHOST_USER_SET_PROTOCOL_FEATURES, a backend should enable the
protocol features immediately.
(2) If VHOST_USER_F_PROTOCOL_FEATURES hasn't been set, upon receiving
VHOST_USER_SET_PROTOCOL_FEATURES, a backend should store those
feature bits, but not actually consider them to be enabled until
after VHOST_USER_SET_FEATURES has been received (presumably
containing VHOST_USER_F_PROTOCOL_FEATURES).
The reason I bring this up is that QEMU appears to interpret it as (1),
while the vhost-user-net backend in Intel's cloud-hypervisor[1]
interprets it as (2). So I'm looking for a clarification.
[1]: https://github.com/cloud-hypervisor/cloud-hypervisor
Thanks in advance.
